Method for preparing alkali cellulose



Feb. 28, 1950 Filed NOV. 26, 1946 W 0 m 0 G 6 n m 0.\

iatented Feb. 28,1950

METHOD FOR PREPARING ALKALI CELLULOSE Johannes G. Weeldenburg, Velp, Netherlands, as-

, signor to American Enka Corporation, Enka,

N. C., a corporation of Delaware Application November 26, 1946, Serial No. 712,407 In Germany July 9, 1942 Section 1, Public Law .690, August 8, 1946 Patent expires July 9, 1962 This invention relates to the preparation of alkali cellulose and is more particularly concerned with a method and apparatus for continuously treating succeeding portions of a moving web of cellulose by spraying it with alkali at one or more places.

A large number of methods have been developed for the preparation of alkali cellulose to be used in the manufacture of artificial fibers from viscose. According to these methods the raw cellulose, either as cotton linters or as wood pulp, has been contacted with a suitable mercerizing lye. In some cases the cellulose has been dried before contacting with the alkali lye and in others it has been treated with the lye while still in the wet condition in which it is produced in the cellulose manufacturing plants. The various methods outlined above have been adopted to varying degrees by the rayon industry but efforts are still being made to further simplify the process by reducing the time required to complete the preparation of the alkali cellulose and by increasing the recovery of the lye used in the process.

It is therefore an object of this invention to provide a method and apparatus for the high speed continuous manufacture of alkali cellulose from raw cellulose such as in the form of wood pulp or cotton linters.

A further object of this invention is to remove the hemicelluloses from a continuous web of pulp or linters in such manner that the material is uniformly subjected to the action of the caustic while the used caustic may be recovered for purification in a simple and efiicient manner.

Other objects and advantages of this invention will be apparent upon consideration of the fol lowing detailed description of a preferred form thereof in conjunction with the annexed drawing wherein the single figure is a schematic view in side elevation of apparatus for the continuous manufacture of alkali cellulose in accordance with the present invention.

In the continuous production of alkali cellulose in accordance with the teachings of the present invention, the cellulose is obtained in wet condition and a continuous web 8 thereof is wound into a roll 9 which is then mounted for rotation on a holder In. The web 8 is drawn from the roll 9 for treatment with alkali and to this end pairs of driven rollers H and 12 are provided. These rollers draw off the web from the holder Ill, and, in passage, between the holder and the pairs of rollers II and I2 succeeding portions of the web 8 are passed over annular perforated 1 Claim. (Cl. 260-333) screens [3 and I4 which are mounted for rotation at l5 and I6 respectively. The screens l3 and I4 are provided at each margin with circular discs I! and [8 which, with the respective screens, define generally drum-like structures. In its passage over screens I 3 and I4, succeeding portions of the web 8 are sprayed with an alkali lye which is supplied from nozzles [9. This lye is drawn through the web 8 by applying suction within the drum-like structures defined by the screens and their discs. Thus, the cellulose is converted to alkali cellulose and the excess lye is removed by the suction lines indicated diagrammatically at 20 and 2|. The pairs of draw off rollers II and [2 function also to press out excess lye and to reduce the web to the required uniform weight. Moving supports such as conveyor belts 22, 23, 24, and 25 serve to guide and support the cellulose sheet in those zones where it does not contact the revolving screens or the draw off rollers.

The inventive method may be carried out in accordance with the counter-current principle, whereby the cellulose Web is first sprayed with a lye which has been used once or several times, and is thereafter immediately sprayed with a fresh lye.

The operation may be carried out in such a manner that in the beginning a more diluted lye (for example, 5 to 7%) Or a more concentrated lye (for example, 20 to 25%) is employed, and at the end of the step the web is sprayed with a lye of the usual mercerizing concentration.

One mode of practicing the present invention involves spraying a dipping lye of approximately 18% concentration through the nozzles I9. The lye is sucked through the wet cellulose layer due to the action of the vacuum, whereby the lye displaces the water therefrom. As a result of this, the water is removed from the cellulose sheet in a short time and the cellulose is converted into alkali cellulose. The length of time of this reaction can be regulated by the selection of the diameter and the velocity of rotation of the revolving screens as well as by the intensity of the spraying with lye and the concentration of the same. An acceleration of the alkalizing reaction can, of course, be effected by increasing the temperature of the dipping lye. Where only a single revolving screen is used instead of the several, as illustrated, it will be understood that the strength of the vacuum will be adjusted accordingly.

Care must be exercised to insure that the lye is sprayed on the cellulose sheet in such a way 3 as to avoid the separation of cellulose particles at the edge of the sheet.

If the cellulose sheet is sprayed at all places with a lye of the usual mercerizing concentration (18%), the lye is highly diluted in the beginning by the water from the cellulose web, which, as obtained from the cellulose manufacturer, usually has a Water content of approximately 50%. The diluted lye has no mercerizing action; however, it promotes the solution of the accompanying substances of the cellulose, which as known, are more soluble in a lye of 5 to 7% concentration than in a lye of 18% concentration. This refining effect can be enhanced by employing at the beginning of the operation a more diluted lye (for example, 5 to 7% concentration) and later in the operation a lye of approximately 18% concentration.

It is not important to remove entirely the accompanying substances from the cellulose, and if the mercerizing action is to take place from the start of the treatment, the cellulose web can be sprayed first with a more concentrated lye, for example, of 20 to 25% concentration. The concentration of said lye is selected so that it is lowered just to the mercerizing concentration by the water contained in the cellulose sheet. As soon as the water has been displaced, the usual concentration of approximately 18% is employed for the continued operation.

The present method has several advantages over the hitherto known methods, particularly in view of the fact that the cellulose plants produce cellulose sheets with a substantially constant cellulose content per square meter, so that the alkali cellulose sheet, made from said cellulose sheet, always contains the same amount of cellulose. However, if a method is used employing cellulose shreds or flakes, that is, if an operation is carried out by means of a so-called cellulose-lye slurry, it is very difficult to obtain a uniform alkali cellulose at any time.

An enrichment of hemi-cellulose or the like in the lye is obtained by employing the countercurrent principle to convert cellulose into alkali cellulose, because lyes which have already been used can be introduced again into the operation with the result that smaller quantities of lye are required to remove the whole amount of hemicellulose from the cellulose, than in the event that the operation is carried out by continually working with pure lye. As a result of this, the regeneration of the lye, for example, by dialysis, is extremely facilitated.

What is claimed is:

A method for the preparation of alkali cellulose in a continuous operation which comprises passing a web of raw cellulose through a plurality of treating zones and, during its passage therethrough, successively spraying the web first with a lye solution selected from the class consisting of lye solutions having a concentration of 20 to 25% and lye solutions having a concentration of 5 to 7%, and then with a lye solution having a mercerizing concentration whereby the cellulose is converted into alkali cellulose, and the web is substantially purified and mercerized, subjecting the web to the action of a vacuum in the said treating zones to simultaneously draw the liquids through the web from one side thereof to the other and recover the excess lye, and subsequently pressing the web to the desired weight,

J OHANNES- G. NEELDENBURG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,667,408 Allen Apr. 24, 1928 1,728,471 Bratring Sept. 17, 1929 1,884,486 Zavertnik Oct. 25, 1932 2,005,811 Steimmig June 25, 1935 2,274,463 Stoeckly et al Feb. 24, 1942 

